1. Field of the Invention
The present invention relates to a multicast service of a 3GPP universal mobile telecommunications system (UMTS) system and, more particularly, to a method for managing a multicast group according to movement of a terminal.
2. Description of the Background Art
A universal mobile telecommunications system (UMTS) is a third generation mobile communication system that has evolved from a standard known as Global System for Mobile communications (GSM). This standard is a European is standard which aims to provide an improved mobile communication service based on a GSM core network and wideband code division multiple access (W-CDMA) technology.
In December, 1998, the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea formed a Third Generation Partnership Project (3GPP) for the purpose of creating the specification for standardizing the UMTS.
The work toward standardizing the UMTS performed by the 3GPP has resulted in the formation of five technical specification groups (TSG), each of which is directed to forming network elements having independent operations.
More specifically, each TSG develops, approves and manages a standard specification in a related region. Among them, a radio access network (RAN) group (TSG-RAN) develops a specification for the function, items desired, and interface of a UMTS terrestrial radio access network (UTRAN), which is a new RAN for supporting a W-CDMA access technology in the UMTS.
FIG. 1 illustrates an example of the construction of a general UMTS network.
The UMTS is roughly divided into a terminal, a UTRAN and a core network.
The UTRAN includes one or more radio network sub-systems (RNS). Each RNS includes an RNC and one or more Node Bs managed by the RNCs.
Node Bs are managed by the RNCs, receive information sent by the physical layer of a terminal (e.g., mobile station, user equipment and/or subscriber unit) through an uplink, and transmit data to a terminal through a downlink. Node Bs, thus, operate as access points of the UTRAN for terminal.
The RNCs perform functions which include assigning and managing radio resources, and operate as an access point with respect to the core network.
The UTRAN constructs and maintains a radio access bearer (RAB) for communication between the terminal and the core network. The core network requests end-to-end quality of service (QoS) requirements from the RAB, and the RAM supports the QoS requirements the core network has set. Accordingly, by constructing and maintaining the RAB, the UTRAN can satisfy the end-to-end QoS requirements.
The services provided to the specific terminal is roughly divided into a circuit switched service and a packet switched service. For example, a general voice phone call service belongs to the circuit switched service, while a Web browsing service through an Internet connection is classified as the packet switched service.
In case of supporting the circuit switched service, the RNC is connected to the MSC of the core network, and the MSC is connected to a GMSC (Gateway Mobile Switching Center) managing a connection to other networks.
Meanwhile, in case of the packet switched service, services are provided by a SGSN (Serving GPRS Support Node) and a GGSN (Gateway GPRS Support Node) 37 of the core network.
The SGSN supports a packet communication going toward the RNC, and the GGSN 37 manages connection to other packet switched networks (i.e, the Internet network).
As the 3GPP system has decided to provide a multimedia broadcast multicast service (MBMS), a fresh service of Release 6, 3GPP TSG SA (Service and System Aspect defines network elements required for the MBMS service and functions of each network element.
A cell broadcast service the conventional Release 99 has provided is limited to a service that a text type short message is broadcast to a certain area. Comparatively, the MBMS service provided by the Release 6 is an advanced service that not only broadcasts a multimedia but also multicasts the multimedia to terminals (UEs) which have subscribed for the corresponding service.
The MBMS will now be described in detail.
The MBMS, a downward-dedicated service, provides a streaming or background service to plural terminals by using a common or dedicated downward channel. The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service transmitting multimedia data to every user located in a broadcast area, whereas the MBMS multicast mode is a service transmitting multimedia data to a specific user group located in a multicast area. The broadcast area signifies a broadcast service available area, and the multicast area signifies a multicast service available area.
Users who desire to receive the MBMS service should receive a service announcement and a service notification provided by a network. The service announcement means informing the terminal of a list of services to be provided and its related information, and the service notification means informing the terminal of information on broadcast data to be transmitted.
Especially, if the user intends to receive the multicast mode MBMS service, he/she should be admitted to a multicast subscription group. The multicast subscription group means a group of users who has finished an admission procedure. Once the user is admitted to the multicast subscription group, he/she can join a multicast group to receive a specific multicast service. In this case, the multicast group signifies a user group receiving the specific multicast service, and ‘joining’ means joining the multicast group gathered to receive the specific multicast service.
The joining behavior is in other way called a MBMS multicast activation. Accordingly, the user can receive the specific multicast data through the MBMS multicast activation or the joining behavior.
FIG. 2 shows a schematic network structure for providing the MBMS service.
As shown in FIG. 2, a broadcast multicast-service center (BM-SC) serves to schedule MBMS contents inputted from a contents provider. A cell broadcast center (CBC) is an entity (a physical or virtual unit handling a specific service) for providing an existing CBC service, that is, for broadcasting a text type short message to a certain area, and can be used for a service announcement of the MBMS service.
Meanwhile, in the case of the packet switched service, the MBMS service is provided by an SGSN (Serving GPRS Support Node) and a GGSN (Gateway GPRS Support Node) of the core network. The SGSN supports a packet communication toward a serving RNC (SRNC) of the UTRAN, and the GGSN manages connection to other packet switched networks such as the Internet through a border gateway (BG).
In the UMTS system, a GTP (GPRS Tunneling Protocol) layer is used to support transmission of the packet data. Specifically, the GTP layer is especially used for transmitting data of a service area. Thus, the GGSN manages a data transmission tunnel through the GTP layer in the existing UMTS packet domain, and generates and manages an MBMS context for the MBMS service.
FIG. 3 illustrates a transmission procedure of an MBMS data.
As shown in FIG. 3, data to be transmitted to members of the multicast group is delivered from an MBMS data source to the GGSN through an IP multicast, and the GGSN generates a GTP tunnel and transmits an MBMS data to the SGSNs which manage users subscribed for the corresponding multicast service. Each SGSN routes the MBMS data to each RNC managing corresponding users, and the RNC transmits the received MBMS data to a corresponding user cell (the area managed by one Node B).
Accordingly, the specific MBMS service user located in the cell, that is, the specific terminals located in the corresponding multicast area, can be provided with the MBMS service upon receiving the MBMS data.
If the BM-SC includes the function of the GGSN, the MBMS data can be directly delivered to the SGSN without passing through the GGSN, and the data would be transmitted to the other entities in the same manner.
As mentioned above, the MBMS service is divided into the broadcast mode service and the multicast mode service. Unlike the broadcast mode service which broadcasts to all the area, the multicast mode service transmits data only to the users (terminals) admitted to the multicast group, of which the data is provided in a unidirectional point-to-multipoint transport method.
When the multicast service is provided, information on which multicast group a user terminal currently belongs to is necessary. In addition, unlike a cable network, the user terminal is moved in the radio network, so that management of the multicast group according to the mobility of the terminal is requisite. If a user terminal moves while being provided with the MBMS service, the mobility information of the corresponding terminal should be sent to a multicast group managing entity.
However, currently, the 3GPP defines only the requirements for the MBMS service, and no substantial matters have been discussed as to what information should be delivered between elements of the network nor as to on the basis of what information which element of the network should manage the multicast group, and in addition, as to whether the mobility information of the terminal should be unconditionally delivered to the entity managing the multicast group if the terminal is moved while being provided with the multicast service.
Therefore, if the terminal being currently provided with the multicast service is moved, there is a possibility that the service provided to the terminal is interrupted. In addition, if the mobility information of the all the terminals is unconditionally delivered to the entity managing the multicast group, the network resource is not effectively used due to the unnecessary signaling.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.